In 1987, E. Yablonovitch of Bell laboratory of the United States and S. John of Princeton University independently put forward the concept of photonic crystal respectively in discussion about how to suppress spontaneous radiation and in discussion about a photonic localization. The photonic crystal is a substance structure formed by periodically arranging dielectric materials in a space, and is usually an artificial crystal composed of two or more materials with different dielectric constants.
In a frequency domain, with regard to a TE wave or a TM wave propagating in any direction, a frequency interval with an electromagnetic field state density of zero is defined as a TE complete bandgap or a TM complete bandgap of a photonic crystal, and a frequency interval which is the TE complete bandgap and the TM complete bandgap simultaneously is called as an absolute bandgap of the photonic crystal. A photonic crystal with a complete bandgap or an absolute bandgap is designed, and is capable of simply and effectively regulating and controlling the macroscopic electromagnetic properties of a dielectric, including selecting a frequency band for propagating an electromagnetic wave, a mode and a transmission path and controlling the absorption or radiation and other properties of the dielectric as a basis of controlling the movement of photons and of producing various photonic devices.
With regard to each of the various photonic crystal devices, the wider a photonic bandgap is, the better the performance of the device is. For example, the wider a photonic bandgap is, the wider a working frequency band of a photonic crystal waveguide is, the lower the transmission loss is, the higher the quality factors of a photonic crystal resonant cavity and a laser device are, the better the constraint effect of a photonic crystal on spontaneous radiation is, the higher the reflectivity of a photonic crystal reflector is, and the like. The photonic crystal with a complete bandgap and an absolute bandgap has a photonic bandgap with regard to lights in different propagation directions.
In the prior art, a relatively large bandgap is obtained by virtue, of triangular lattices, hexagonal lattices and other non-square lattice structures; however, in an integrated optical circuit of a photonic crystal, it is not easy to provide optical circuit integration; and in the prior art, a square lattice photonic crystal has a quite small absolute bandgap width.